1. Field of the Invention
The present invention relates to fuel supply systems used mainly for engines of vehicles.
2. Description of the Related Art
A conventional fuel supply system is shown in Japanese Laid-Open Patent Publication No. 2001-90624. FIG. 6 is a schematic structural view showing the conventional fuel supply system disclosed in this publication. As shown in FIG. 6, fuel supply system 200 includes a fuel tank 201, from which fuel is drawn and pressurized by a fuel pump 202 and passes through a fuel filter 204 and a supply pipe 203. Then the fuel is injected from each injection valve 205 into a combustion chamber of an internal combustion engine (hereinafter called “engine”). A fuel pressure regulating device 207 opens and closes a reflux control valve 224 in accordance with control signals from a control unit 229, and accordingly, pressure of fuel (hereinafter called “fuel pressure”) supplied to each injection valve 205 may be switched between high pressure and low pressure.
More specifically, the fuel pressure regulating device 207 opens the reflux control valve 224, for instance when the engine starts to introduce the fuel into a control pressure chamber 208B of a pressure regulator 208, for increasing the pressure inside the control pressure chamber 208 B. Accordingly, the fuel pressure inside a fuel pressure regulating chamber 208A of the pressure regulator 208 is increased, and fuel pressure inside the supply pipe 203 communicating with the fuel pressure regulating chamber 208A is increased. Due to this, the fuel pressure supplied to each injection valve 205 becomes high to enhance atomization of the injected fuel, and accordingly, starting performance of the engine is improved. The fuel inside the fuel regulating chamber 208A is then refluxed into a fuel tank 201 via a delivery pipe path 223. The reflux control valve 224 is closed after starting the engine so that the pressure inside the pressure control chamber 208B of the pressure regulator 208 is decreased. Therefore, the fuel pressure inside the fuel regulating chamber 208A and the supply pipe 203 is decreased. Accordingly, the fuel pressure supplied to each injection valve 205 becomes low, and therefore, load on the fuel pump 202 etc. is reduced.
In the conventional fuel supply system (see FIG. 6), the fuel introduced into the fuel pressure regulating chamber 208A of the pressure regulator 208 during the pressurization, flows into the fuel tank 201 via the delivery pipe path 223. As a result, the efficiency of pump is decreased due to the large loss of fuel flow volume.
Therefore, there has been a need for a fuel supply system that can prevent the loss of fuel flow volume during the pressurization, which can improve the efficiency of the pump.